Liquid crystal display device

ABSTRACT

The liquid crystal display device includes: a TFT substrate including scanning lines extending in a first direction and being arranged in a second direction, Video signal lines extending in the second direction and being arranged in the first direction, pixel electrodes arranged in regions surrounded by the scanning lines and the video signal lines, and common electrodes formed with an insulating film arranged between the common electrodes and the pixel electrodes; a counter substrate opposed to the TFT substrate; and a liquid. crystal. The first common electrode extends between the first and second scanning lines in the first direction, and the second common electrode extends between the second and third scanning lines in the first direction. The first and second common electrodes are electrically connected by a bridge. The bridge covers the first video signal line without covering the second video signal line, when seen in a plan view.

CLAIM OF PRIORITY

The present application claims priority from Japanese Patent ApplicationJP 2015-99820 filed on May 15, 2015, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to a display device and, in particular, toa high-resolution liquid crystal display device.

(2) Description of the Related Art

In liquid crystal devices, a TFT substrate on which pixels eachincluding a pixel electrode, and a thin film transistor (TFT), forexample, are arranged in a matrix and a counter substrate are arrangedto be opposed to each other. A liquid crystal is sandwiched between theTFT substrate and the counter substrate. A transmittance of light ofliquid crystal molecules is controlled on a pixel-by-pixel basis,thereby an image is formed.

One of problems of the liquid. crystal display devices is viewing anglecharacteristics. An IPS (In Plane Switching) liquid crystal displaydevice rotates the liquid crystal molecules by an electric fieldparallel to the substrates to control the light transmittance of theliquid crystal, and is excellent in viewing angle characteristics.Meanwhile, the resolution of the liquid crystal display devices, inparticular, small and medium-sized liquid crystal display devices isincreasing.

With the increase of the resolution, a ratio of an area of a diameter ofa through hole for allowing the pixel electrode to come in contact witha source electrode of the TFT, formed on the TFT substrate side, to anentire area of a pixel is also increased. Japanese Unexamined PatentApplication Publication No. 2014-146039 describes a structure of thethrough hole in the IPS liquid crystal display device.

SUMMARY OF THE INVENTION

Liquid crystal display panels used for smartphones, tablets, and thelike have been demanded to have a high resolution. These products have ahorizontal pitch of 30 μm or less per pixel. Note that each of a redpixel, a green pixel, a blue pixel, and the like is referred to as apixel in this specification, although a set of the red pixel, the greenpixel, the blue pixel, and the like is referred to as a pixel in somecases.

Meanwhile, the IPS liquid crystal display devices are used in order toimprove the viewing angle characteristics. In the IPS type, a structureis most commonly used in which a stripe or comb-teeth pixel electrode isarranged on a common electrode formed in a plane with an insulating filmtherebetween. In this IPS type, it is necessary to form the through holein the insulating film that is thick in order to connect the TFT and thepixel electrode in each pixel. Therefore, the diameter of this throughhole becomes large.

A potential that is common to the pixels has to be applied to the commonelectrode formed in a plane. As the pixel pitch is smaller, the ratio ofthe area occupied by the through hole to the entire area of the pixel islarger. Meanwhile, the common electrode has to be formed in a regionother than the through hole, and therefore has a bridge shape betweenthe horizontally adjacent through holes. Due to the existence of thisbridge and the through hole, reduction of the pixel pitch is limited.Further, when the screen size is increased, the resistance of the commonelectrode becomes a problem. This is because the common electrode isformed of ITO (Indium Tin Oxide) that has a relatively large specificresistance.

The present invention has been made for providing a liquid crystaldisplay device having a large screen that can achieve a pixel pitchcorresponding to a high resolution while suppressing increase of aresistance of a common electrode.

(1) According to one aspect of the present invention, a liquid crystaldisplay device includes: a TFT substrate including scanning linesextending in a first direction and being arranged in a second direction,video signal lines extending in the second direction and being arrangedin the first direction, pixel electrodes arranged in regions surroundedby the scanning lines and the video signal lines, and common electrodesformed with an insulating film arranged between the common electrodesand the pixel electrodes; a counter substrate opposed to the TFTsubstrate; and a liquid crystal sandwiched between the TFT substrate andthe counter substrate. A first common electrode extends between a firstscanning line and a second scanning line in the first direction, asecond common electrode extends between the second scanning line and athird scanning line in the first direction, and the first commonelectrode and the second common electrode are electrically connected bya bridge. The bridge covers a first video signal line without covering asecond video signal line, when seen in a plan view.

(2) In the liquid crystal display device described in (1), the bridge isformed by a metal wiring.

(3) In the liquid crystal display device described in (1), a first,pixel is arranged between. the first video signal line and the secondvideo signal line, a second pixel is arranged between the first videosignal line and the first video signal line, and a width of the firstpixel in the first direction is larger than a width of the second pixelin the first direction.

(4) In the liquid crystal display device described in (1), a columnarspacer is formed in the counter substrate and comes into contact withthe TFT substrate above the second video signal line.

(5) According to another aspect of the present invention, a liquidcrystal display device includes: a TFT substrate including scanninglines extending in a first direction and being arranged in a seconddirection, video signal lines extending in the second direction andbeing arranged in the first direction, pixel electrodes arranged inregions surrounded by the scanning lines and the video signal lines, andcommon electrodes formed with a second insulating film arranged betweenthe common electrodes and the pixel electrodes; a counter substrateopposed to the TFT substrate and including a columnar spacer; and aliquid crystal sandwiched between the TFT substrate and the countersubstrate. A first common electrode extends between a first scanningline and a second scanning line in the first direction, a second commonelectrode extends between the second scanning line and a third scanningline in the first direction, and the first common electrode and thesecond common electrode are electrically connected by a bridge. Thebridge covers a first video signal line without covering a second videosignal line, when seen in a plan view. The common electrodes are formedabove a first insulating film, and a first electrode is formed below thefirst insulating film. The first insulating film has a first throughhole in a portion corresponding to the first electrode, and a connectionITO formed simultaneously with the common electrodes covers the firstthrough hole and is insulated from the common electrodes. The secondinsulating film has a second through hole formed to correspond to theconnection ITO. A pixel electrode is electrically connected to the firstelectrode. The connection ITO has a width in the first direction, and acenter of the connection ITO in the first direction is located on a sideof a center of a gap between the first video signal line and the secondvideo signal line, the side being closer to the second video signalline.

(6) In the liquid crystal display device described in (5), the bridge isformed by a metal wiring.

(7) In the liquid crystal display device described in (5), a first pixelis arranged between the first video signal line and the second videosignal line, a second pixel is arranged between the first video signalline and the first video signal line, and a width of the first pixel inthe first direction is larger than a width of the second pixel in thefirst direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a liquid. crystal display device to which thepresent invention is applied.

FIG. 2 is a cross-sectional view, taken along line A-A in FIG. 1.

FIG. 3 is a plan view of a through hole and a nearby portion thereof inFIG. 1.

FIG. 4 is a plan view of a liquid crystal display device according to afirst embodiment.

FIG. 5 is a cross-sectional view, taken along line B-B in FIG. 4.

FIG. 6 is a plan view illustrating a feature of the first embodiment.

FIG. 7 is a cross-sectional view illustrating another form of the firstembodiment.

FIG. 8 is a plan view illustrating a feature of a second embodiment.

FIG. 9 is a cross-sectional view, taken along line C-C in FIG. 8.

FIG. 10 is another plan view illustrating the feature of the secondembodiment.

FIG. 11 is a plan view illustrating a feature of a third embodiment.

FIG. 12 is a cross-sectional view in a fourth embodiment.

FIG. 13 is a schematic cross-sectional view illustrating an example of acause of an occurrence of scraping of an alignment film.

FIG. 14 is a plan view illustrating a feature of the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in detail below, referring toembodiments.

First Embodiment

FIG. 1 is a plan view of a liquid crystal display device employing IPStechnology used in the present invention, illustrating a pixelstructure. There are various types of the IPS technology. In one type, acommon electrode is formed in a plane, a comb-teeth pixel electrode isarranged on the common electrode with an insulating film arrangedtherebetween, and liquid crystal molecules are rotated by an electricfield generated between the pixel electrode and the common electrode.This type can achieve a relatively large transmittance and is thereforecurrently the main stream.

In FIG. 1, scanning lines 10 extend in a transverse direction and arearranged in a longitudinal direction with a predetermined pitch. Thelongitudinal pitch of the scanning lines 10 corresponds to thelongitudinal size of a pixel. Video signal lines 20 extend in thelongitudinal direction and are arranged in the transverse direction witha predetermined pitch. The transverse pitch. of the video signal lines20 corresponds to the transverse size of the pixel.

In the pixel, a stripe pixel electrode 111 extends in the longitudinaldirection. In FIG. 1, the pixel electrode has a form of a single stripebecause the pixel pitch is as small as 30 μm or less. However, when thepixel pitch is large, a comb-teeth electrode having a slit is formed asthe pixel electrode.

A video signal is supplied to the pixel electrode 111 from acorresponding video signal line 20 via a through hole and a TFT. In FIG.1, the video signal line and a semiconductor layer 103 are connected viathe through hole 120. The semiconductor layer 103 extends below thevideo signal line 20, passes below the scanning line 10, is then bent,passes below the scanning line 10 again, and is connected to a contactelectrode 107 via a through hole 140. The contact electrode 107 isconnected to the pixel electrode via through holes 130 and 131. In aportion where the semiconductor layer 103 passes below the scanning line10, the TFT is formed. In this case, the scanning line 10 also serves asa gate electrode. Therefore, in FIG. 1, two TFTs are formed from thevideo signal line 20 to the pixel electrode 11, that is, a so-calleddouble-gate method is applied.

In FIG. 1, a direction of an alignment axis 115 formed in an alignmentfilm is at an angle of θ with respect to the extending direction of thepixel electrode 111. The reason why the angle θ is formed is to define adirection of rotation of liquid crystal molecules when an electric fieldis applied to the pixel electrode 111. θ is from about 5° to about 15°,preferably from 7° to 10°. Note that in some cases the direction of thealignment axis 115 is along the longitudinal direction in FIG. 1 and theextending direction of the pixel electrode 111 is inclined by θ. FIG. 1shows a case where dielectric anisotropy of the liquid crystal moleculesis positive. The angle of the alignment axis in the case where thedielectric anisotropy of the liquid crystal molecules is negative is anangle rotated from that in FIG. 1 by 90°.

In FIG. 1, a common electrode is formed on an entire surface except. forthe through hole and its nearby portion. The common electrode 109 on theupper side of the scanning line and that on the lower side of thescanning line in FIG. 1 are connected via a common-electrode bridge1091. The existence of the common-electrode bridge 1091 is a problem inorder to increase the resolution and reduce the pixel pitch.

FIG. 2 is a cross-sectional view, taken along line A-A in FIG. 1. TheTFT in FIG. 2 is a so-called top gate TFT using LIPS (Low TemperaturePoli-Si) as a semiconductor material. Meanwhile, in the case of usinga-Si as the semiconductor material, a so-called bottom gate TFT isfrequently used. The following description is made referring to the caseof using the top gate TFT as an example, but the present invention canbe also applied to the case of using the bottom gate TFT.

In FIG. 2, a first underlying film 101 of SiN and a second underlyingfilm 102 of SiO₂ are formed on a glass substrate 100 by CVD (ChemicalVapor Deposition). The first underlying film 101 and the secondunderlying film 102 have a role of preventing impurities from the glasssubstrate 100 from contaminating the semiconductor layer 103.

The semiconductor layer 103 is formed on the second underlying film 102.This semiconductor layer 103 is obtained by depositing an a-SI film onthe second underlying film 102 by CVD and then converting it to apoly-Si film by laser annealing. This poly-Si film is patterned byphotolithography.

A gate insulating film 104 is formed on the semiconductor layer 103.This gate insulating film 104 is an SiO₂ film deposited by using TEOS(Tetraethoxysilane). This film is also deposited by CVD. A gateelectrode 105 is formed on the gate insulating film 104. The gateelectrode 105 is formed by the scanning line 10. The gate electrode 105is formed by a MoW film, for example. When the resistance of the gateelectrode 105 or the scanning line 10 has to be reduced, Al alloy isused.

Then, an interlayer insulating film 106 is formed of SiO₂ or SiN tocover the gate electrode 105. The interlayer insulating film 106 isformed for insulating the gate electrode 105 and the contact electrode107 from each other. The semiconductor layer 103 is connected to thevideo signal line 20 via the through hole 120 formed in the gateinsulating film 104 and the interlayer insulating film 106. Also, athrough hole 140 is formed in the interlayer insulating film 106 and thegate insulating film 104 for connecting a source portion S of the TFT tothe contact electrode 107. The through hole 120 and the through hole 140in the interlayer insulating film 106 and the gate insulating film 104are formed simultaneously.

The contact electrode 107 is formed on the interlayer insulating film106. The semiconductor layer 103 extends below the video signal line 20and passes below the scanning line 10, that is, the gate electrode 105twice, as illustrated in FIGS. 1 and 2. In the portion where thesemiconductor layer 103 passes below the scanning line 10, the TFTs areformed. In other words, the source portion S and a drain portion D ofthe TFT are formed to sandwich the gate electrode 105 therebetween, whenseen in a plan view. The contact electrode 107 is connected to thesemiconductor layer 103 via the through hole 140 formed in theinterlayer insulating film 106 and the gate insulating film 104.

The contact electrode 107 and the video signal line 20 are formedsimultaneously in the same layer. For the contact electrode 107 and thevideo signal line 20, AlSi alloy is used, for example, for achieving asmall resistance. In this case, a structure sandwiching AlSi alloybetween a barrier layer of MoW, for example, and a cap layer isemployed, because AlSi alloy may cause hillocks or diffusion of Al toanother layer.

An organic passivation film 108 is formed to cover the contact electrode107, the video signal line 20, and the interlayer insulating film 106.The organic passivation film 108 is formed of photosensitive acrylicresin. Other than the acrylic resin, silicone resin, epoxy resin, andpolyimide resin can be used for the organic passivation film 108, forexample. The organic passivation film 108 serves as a flattening filmand is therefore formed to be thick. The thickness of the organicpassivation film 108 is from 1 μm to 4 μm. In most cases, the thicknessof the organic passivation film 108 is from about 2 μm to about 3 μm.

The through hole 130 and the through hole 131 are respectively formed inthe organic passivation film 108 and a capacity insulating film 110described later for achieving electric continuity between the pixelelectrode 111 and the contact electrode 107. Photosensitive resin isused for the organic passivation film 108. The photosensitive resin isapplied and is then exposed with light. After the light exposure, only aportion exposed with light is dissolved by a specific developing agent.That is, the use of the photosensitive resin can eliminate formation ofphotoresist. After the through hole 130 is formed in the organicpassivation film 108, firing is performed at about 230° C., so that theorganic passivation film 108 is completed.

Subsequently, a transparent conductive film forming the common electrode109, e.g., an ITO (Indium Tin Oxide) film, is formed by sputtering, andis patterned so that the ITO film is removed from the through hole 130and a portion around the through hole 130. The common electrode 109 canbe formed in a plane to be common to the pixels. However, the commonelectrode 109 has to be formed in a portion other than the through hole130. Therefore, in the case of reducing the pixel pitch, thecommon-electrode bridge 1091 in FIG. 1 is a problem.

In a second embodiment of the present invention, a connection ITO 40 isformed to cover the through hole 130 simultaneously with the commonelectrode 109, as illustrated in FIG. 9. The reason for this is toensure a margin for achieving contact between the contact electrode 107and the pixel electrode. In this case, it is necessary to insulate theconnection ITO 40 and the common electrode 109 from each other.

Returning to FIG. 2, SiN forming the capacity insulating film 110 isdeposited by CVD on the entire surface. Then, the through hole 131 isformed in the capacity insulating film 110 for achieving electriccontinuity between the contact electrode 107 and the pixel electrode 111in the through hole 130.

Then, an ITO film is formed by sputtering and is patterned to form thepixel electrode 111. An example of the planar shape of the pixelelectrode 111 is shown in FIG. 1. An alignment film material is appliedonto the pixel electrode 111 by flexography or ink jet printing, forexample, and is fired, so that the alignment film 112 is formed. As analignment process of the alignment film 112, rubbing or opticalalignment using polarized ultraviolet rays is used.

When a voltage is applied across the pixel electrode 111 and the commonelectrode 109, lines of electric force are generated as illustrated inFIG. 2. This electric field rotates liquid crystal molecules 301, andcontrols the amount of light passing through a liquid crystal layer 300on a pixel-by-pixel basis. In this manner, an image is formed.

In FIG. 2, a counter substrate 200 is arranged with the liquid crystallayer 300 sandwiched between the counter substrate 200 and the TFTsubstrate. Inside the counter substrate 200 is formed a color filter201. As the color filter 201, any one of red, green, and blue colorfilters is formed for every pixel, so that a color image is formed. Ablack matrix 202 is formed between the color filter 201 and the adjacentcolor filter 201 to improve a contrast of the image. The black matrix202 also nerves as a light shielding film of the TFT that prevents aphotocurrent from flowing in the TFT.

An overcoat film 203 is formed to cover the color filter 201 and theblack matrix 202. Because the surface of the color filter 201 and theblack matrix 202 is uneven, the overcoat film 203 smoothens the surface.An alignment film 112 is formed on the overcoat film 203 to define aninitial alignment of the liquid crystal molecules. As the alignmentprocess of the alignment film 112, rubbing or optical alignment is usedas in the alignment film 112 on the TFT substrate 100 side.

The above-described structure is merely an example. For example, aninorganic passivation film of SiN or the like is formed between thecontact electrodes 107 and the video signal lines 20 in the TFTsubstrate 100 in some products.

FIG. 3 is an enlarged plan view of the through hole 130 and its nearbyportion in FIG. 1. The pixel electrode is omitted in FIG. 3. In FIG. 3,a region where the common electrode 109 is not formed is provided aroundthe throughhole 130 to have a rectangular hole shape. Thus, the commonelectrode 109 on the upper side of the through hole 130 and that on thelower side are connected by the common-electrode bridge 1091. When thepixel pitch is reduced, the existence of the common-electrode bridge1091 becomes a problem. More specifically, because ITO forming thecommon electrode 109 has a large resistivity, the width of thecommon-electrode bridge 1091 has to be larger than those of the videosignal line 20 and the semiconductor layer 103. Therefore, the existenceof the common-electrode bridge 1091 is a problem, in particular, in thecase of reducing the horizontal pixel pitch.

FIG. 4 is a plan view of the pixel in the case where the presentembodiment is applied. FIG. 4 is different from FIG. 1 in a method ofconnecting, the upper common electrode 109 and the lower commonelectrode 109 in FIG. 4. In FIG. 4, the common electrodes 109 extend inthe transverse direction in stripes on the upper and lower sides of thethrough hole 130. A common metal wiring 30 extends above the commonelectrode 109 in the longitudinal direction to cover the video signalline 20. The common metal wiring 30 is used for reducing the resistanceof the common electrode 109.

In FIG. 4, the upper common electrode 109 and the lower common electrode109 are electrically connected by the common metal wiring 30. That is,the common metal wiring 30 serves as the bridge 1091 between the uppercommon electrode 109 and the lower common electrode 109. The commonmetal wiring 30 is formed of a metal, for example, MoCr alloy, MoWalloy, or Al alloy, and therefore has a smaller resistance than ITO.Thus, the width of the wiring can be made smaller. In other words, theupper common electrode 109 and the lower common electrode 109 can beconnected by the common metal wiring 30 having the smaller width. Alarger feature in FIG. 4 is that the common metal wiring 30 as thebridge 1091 is arranged for every other video signal line 20. Thisarrangement can further reduce the horizontal pixel pitch. The otherstructure in FIG. 4 is the same as that in FIG. 1 and therefore thedescription thereof is omitted.

FIG. 5 is a cross-sectional view, taken along line B-B in FIG. 4, andillustrates a cross-section of a portion where the common metal wiring30 serves as the bridge 1091 between the common electrodes 109 in FIG.4. FIG. 5 is different from FIG. 2 in that the common metal wiring 30extends on the organic passivation film 108 on the left side in a regioncovering the video signal line 20, and is connected to the commonelectrode 109. Other portions in FIG. 5 are the same as those in FIG. 2and therefore the description thereof is omitted.

FIG. 6 is an enlarged plan view of the through hole 130 and its nearbyportion in FIG. 4. The pixel electrode is omitted in FIG. 6. In FIG. 6,the common electrode 109 on the upper side of the through hole 130 andthat on the lower side of the through hole 130 are connected by thecommon metal wiring 30. The common metal wiring 30 is formed to coverevery other video signal line 20. Consequently, the pixel pitch d2 inFIG. 6 is smaller than the pixel pitch d1 in FIG. 3. That is, thestructure in FIG. 6 can be applied to a higher-resolution screen.

FIG. 7 is a cross-sectional view illustrating another form of thepresent invention, corresponding to the cross-section taken along lineB-B in FIG. 4. FIG. 7 is different from FIG. 5 in that the bridge 1091connecting the common electrodes 109 in the region covering the videosignal line 20 has a multilayer structure of the ITO film 109 formingthe common electrode and the common metal wiring 30. Due to themultilayer structure, the resistance of the bridge 1091 can be slightlyreduced, as compared with the resistance in the case of FIG. 5. Further,due to the multilayer structure, tolerance for disconnection of thebridge 1091 can be increased. Note that patterning of the commonelectrode 109 is performed by photolithography and is not burden in theprocess.

In the present embodiment described above, the bridge 1091 connectingthe common electrodes 109 is formed by the common metal wiring 30, andthe common metal wiring 30 is formed to correspond to every other videosignal line 20. However, in a product in which the resistance of thecommon electrode 109 is not a big problem, the bridge 1091 can be formedby ITO forming the common electrode 109 to correspond to every othervideo signal line 20 without using the common metal wiring 30. Also inthis case, reduction of the pixel pitch can be achieved by the existenceof the region including no bridge 1091.

Second Embodiment

FIG. 8 is a plan view of the pixel to which the present invention isapplied, illustrating the through hole 130 and its nearby portion. Thepixel electrode is omitted in FIG. 8. The plan view of the entire pixelin the present embodiment is the same as FIG. 1, and the cross-sectionalview is the same as FIG. 2. FIG. 8 is different from FIG. 3 in aconnection ITO 40 formed in the portion of the through hole 130, and thediameter and location of the through hole 131 formed in the capacityinsulating film 110.

In order to form the through hole 131 in the capacity insulating film110 only at the bottom of the through hole 130 formed in the organicpassivation film 108, it is necessary to make the diameter of thethrough hole 130 large, which is disadvantageous for reducing the pixelpitch. In the present embodiment, the connection ITO 40 formedsimultaneously with the common electrode 109 is used, thereby offeringfreedom of designing the location and shape of the through hole 131formed in the capacity insulating film 110. Due to this, the diameter ofthe through hole 130 formed in the organic passivation film 108 can bereduced.

In FIG. 8, the connection ITO 40 is formed to cover the through hole130. The connection ITO 40 as formed simultaneously with the commonelectrode 109. Therefore, there is no process burden. however, theconnection ITO 40 has to be insulated from the common electrode 109,because the connection ITO 40 is connected to the pixel electrode. Thecapacity insulating film 110 of SiN is formed to cover the connectionITO 40 and the common electrode 109, and the through hole 131 is formedin the capacity insulating film 110. In FIG. 8, the through hole 131 isformed not only at the bottom of the through hole 130 but also on theside face of the through hole 130 and a part of an upper surface of aportion around the through hole 130. Therefore, even in the case wherethe through hole 130 is small, the through hole 131 can be easilyformed.

FIG. 9 is a cross-sectional view, taken along line C-C in FIG. 8. InFIG. 9, the connection ITO 40 is formed to cover the through hole 130 inthe organic passivation film 108. The capacity insulating film 110 isformed to cover the connection ITO 40, and the through hole 131 isformed in the capacity insulating film 110. In this through hole 131,the connection ITO 40 is exposed and is to be connected to the pixelelectrode. As illustrated in FIG. 9, the through hole 131 in thecapacity insulating film 110 can be formed to be large in the presentembodiment, even in the case where the through hole 130 formed in theorganic passivation film 108 is small. Therefore, reliability ofconnection can be improved.

However, the connection ITO 40 has to be insulated from the commonelectrode 109. Because the connection ITO 40 and the common electrode109 are formed in the same layer, a gap g1 between the connection ITO 40and the common electrode 109 has to be sufficiently large when thebridge 1091 connecting the upper common electrode 109 and the lowercommon electrode 109, illustrated in FIG. 8, is formed by the same ITOfilm as that for the common electrode 109. Thus, there is a limit onreduction of the pixel pitch.

In the present embodiment, connection between the upper common electrode109 and the lower common electrode 109 is achieved by the common metalwiring 30, as illustrated in FIG. 10. The common metal wiring 30 isarranged to correspond to every other video signal line. On a side whereno common metal wiring 30 is provided, insulation between the connectionITO 40 and the common electrode 109 or the common metal wiring 30 is nota problem. Therefore, in FIG. 10, it is only necessary to pay attentionto a gap g2 on this side.

Meanwhile, on a side where the common metal ring 30 is provided in FIG.10, the gap g1 between the common ITO 40 and the common metal hang 30has to be ensured. Therefore, a horizontal center position of theconnection ITO 40 is shifted to the side where no common metal wiring 30is provided from the center position of the pixel. Due to this shifting,the transverse diameter of the pixel can be reduced and therefore thepixel pitch can be reduced.

In other words, in the present embodiment, the diameter of the throughhole 130 formed in the organic passivation film 108 can be reduced.Also, the pixel pitch can be further reduced by shifting the center ofthe connection ITO 40 from the center of the pixel, that is, the centerbetween the video signal lines 20.

As in the first embodiment, the bridge 1091 connecting the upper commonelectrode 109 and the lower common electrode 109 can have a multilayerstructure of ITO forming the common electrode 109 and the common metalwiring 30 or a structure including only ITO forming the common electrode109.

Third Embodiment

FIG. 11 is a plan view of the pixel according to a third embodiment,illustrating the through hole 130 and its nearby portion. The basicstructure and the cross-section of the pixel are similar to thoseillustrated in FIGS. 1 and 2. A feature in FIG. 11 is that one of a redpixel, a green pixel, and a blue pixel has a larger horizontal diameterthan those of others. The reason is to handle different requests for awhite tone from customers, for example. In FIG. 11, the diameter of theblue pixel is larger than those of other pixels. That is, B>R=G in FIG.11. However, the red pixel or the green pixel is larger in some cases.

In FIG. 11, the common electrodes 109 extend in stripes in thehorizontal direction on upper and lower sides of the through hole 130.While the upper common electrode 109 and the lower common electrode 109are connected by the common metal wiring 30 as the bridge 1091, thecommon metal wiring 30 for the bridge 1091 is mainly provided only inthe blue pixel having the larger width. The structure of the throughhole 130 in FIG. 11 is the same as that described referring to FIGS. 8to 10. In the through holes 130 arranged on both sides of the commonmetal wiring 30 in FIG. 11, the horizontal center of the connection ITO40 is arranged in a direction away from the common metal wiring 30. Thereason for this is the same as that described in the second embodiment.

With the structure in FIG. 11, the common metal wiring 30 for he bridge1091 is formed in a portion corresponding to the pixel having the largerpixel width, the bridge 1091 is not formed in other portions, and theconnection ITO 40 is formed, so that the diameter of the through hole130 can be reduced. Therefore, the pixel pitch can be reduced.

Also, in FIG. 11, the bridge 1091 formed in the portion corresponding tothe wider pixel can have a multilayer structure of the common metalwiring 30 and ITO forming the common electrode 109 or a structureincluding only ITO forming the common electrode 109, other than thestructure including only the common metal wiring 30, as in the firstembodiment.

Although the bridge electrode is formed only in the portioncorresponding to the pixel having the larger pixel width in FIG. 11, thepresent embodiment is not limited thereto. Even in the case where thered, green, and blue pixels have the same pixel width, the common metalwiring 30 for bridge connection can be provided for every three videosignal lines 20. Also in this case, the center of the connection ITO 40is formed to go away from the bridge 1091, thereby further enhancing theeffect of reduction of the pixel pitch.

In the present embodiment described above, the structure is described inthe case where the connection ITO 40 is formed in the portion of thethrough hole 130. However, according to the present embodiment, thepixel pitch can be reduced as a whole by forming the bridge 1091 mainlyfor the wider pixel, even in a structure including no connection ITO 40.

Fourth Embodiment

It is necessary to define a gap between a TFT substrate and a countersubstrate in a liquid crystal display device. The gap between the TFTsubstrate 100 and the counter substrate 200 is generally defined by acolumnar spacer. FIG. 12 illustrates an example in which the gap betweenthe TFT substrate 100 and the counter substrate 200 is defined by thecolumnar spacer 50 in the present embodiment. The columnar spacer 50formed in the counter substrate 200 defines the gap between the TFTsubstrate 100 and the counter substrate 200. The columnar spacer 50 isformed in the counter substrate 200 simultaneously with the overcoatfilm 203. Another difference between FIGS. 12 and 2 is that the commonelectrode 109 or the bridge 1091 does not exist in a portion of the TFTsubstrate 100 that is to come into contact with the columnar spacer 50.The other structure in FIG. 12 is the same as that in FIG. 2.

A tip of the columnar spacer 50 comes into contact with the alignmentfilm 112 formed in the TFT substrate 100. However, when the alignmentfilm 112 is scraped by this contact, scraped chips cause bright spots.Such scraping can easily occur, especially in the case where a surfaceopposed to the columnar spacer 50, with which the tip of the columnarspacer 50 is to come into contact, is uneven as illustrated in FIG. 13.FIG. 13 illustrates a case where the tip of the columnar spacer 50 comesinto contact with an end portion of the bridge 1091. In a regionincluding a step of the bridge 1091, that is, a region A in FIG. 13, thealignment film 112 can be easily scraped. This bridge 1091 is the ITOfilm formed simultaneously with the common electrode 109 in some casesand is the common metal wiring 30 in other cases.

FIG. 14 is a plan view of the through hole 130 and its nearby portion,illustrating a feature of the present embodiment. In FIG. 14, the pixelelectrode is omitted. In FIG. 14, the columnar spacer 50 comes intocontact with the TFT substrate 100 in a portion where the common metalwiring 30 as the bridge 1091 connecting the upper common electrode 109and the lower common electrode 109 or the ITO film formed simultaneouslywith the common electrode 109 does not exist. With this structure, thestep illustrated in FIG. 13 can be eliminated at the tip of the columnarspacer 50 and it is therefore possible to prevent the alignment film 112from being scraped. The other structure in FIG. 14 is the same as thatin FIG. 6 and therefore the description thereof is omitted.

The structure of the present embodiment can be applied to the structureof the second embodiment illustrated in FIG. 10 and the structure of thethird embodiment illustrated in FIG. 11, for example. In other words,the tip of the columnar spacer 50 can come into contact with a portionof the TFT substrate 100 above the video signal line 20, in which theITO film formed simultaneously with the common electrode 109 or thecommon metal wiring 30 is not formed.

What is claimed is:
 1. A liquid crystal display device comprising: a TFTsubstrate including a gate line, a first video signal line, a secondvideo signal line, a first pixel electrode disposed between the firstvideo signal line and the second video signal line in a plan view, afirst common electrode overlapping the first pixel electrode, and aninsulating film arranged between the first common electrode and thefirst pixel electrode; a counter substrate opposed to the TFT substrate;and a liquid crystal between the TFT substrate and the countersubstrate, wherein the first common electrode is formed by a transparentconductive film, and the first common electrode is electricallyconnected to a metal film, and the metal film overlaps the first videosignal line in a plan view, and a second video signal line has a portionwhich does not overlap the metal film.
 2. The liquid crystal displaydevice of claim 1, wherein the metal film overlaps the gate line.
 3. Theliquid crystal display device of claim 1, further comprising a firstthin film transistor electrically connected to the gate line, the firstvideo signal line, and the first pixel electrode, wherein the first thinfilm transistor has a semiconductor film which is connected to the firstvideo signal line via a first contact hole, and the first contact holeand a part of the semiconductor overlap the metal film.
 4. The liquidcrystal display device of claim 3, further comprising a second thin filmtransistor electrically connected to the gate line and the second videosignal line, and a second pixel electrode, wherein the second pixelelectrode overlaps the first common electrode, wherein the first pixelelectrode is connected to a first contact electrode which is connectedto the first thin film transistor, and the second pixel electrode isconnected to a second contact electrode which is connected to the secondthin film transistor, wherein the metal film is not formed between thefirst contact electrode and the second contact electrode, in a planview.
 5. The liquid crystal display device of claim 1, furthercomprising a second common electrode, wherein the second commonelectrode is separated from the first common electrode, and the secondcommon electrode overlaps a part of the metal film.
 6. The liquidcrystal display device of claim 5, further comprising a first thin filmtransistor electrically connected to the gate line, the first videosignal line, and the first pixel electrode, wherein the first thin filmtransistor has a semiconductor film which is connected to the firstvideo signal line via a first contact hole, and the first contact holeand a part of the semiconductor overlap the metal film between the firstcommon electrode and the second common electrode.
 7. The liquid crystaldisplay device of claim 6, further comprising a second thin filmtransistor electrically connected to the gate line and the second videosignal line, and a second pixel electrode, wherein the second pixelelectrode overlaps the first common electrode, wherein the first pixelelectrode is connected to a first contact electrode which is connectedto the first thin film transistor, and the second pixel electrode isconnected to the second contact electrode which is connected to thesecond thin film transistor, wherein the metal film is not formedbetween the first contact electrode and the second contact electrode, ina plan view.
 8. The liquid crystal display device of claim 1, furthercomprising an organic film, wherein the first pixel electrode and thefirst common electrode are disposed between the organic film and theliquid crystal.
 9. The liquid crystal display device of claim 8, furthercomprising a first thin film transistor electrically connected to thegate line, the first video signal line, and the first pixel electrode,wherein the first thin film transistor has a semiconductor film which isconnected to the first video signal line via a first contact hole, andthe first contact hole and a part of the semiconductor overlap the metalfilm.
 10. The liquid crystal display device of claim 9, wherein thefirst thin film transistor is connected to a first contact electrode,and the first pixel electrode is connected to the first contactelectrode via a second contact hole which is formed in the organic film.11. The liquid crystal display device of claim 10, further comprising asecond thin film transistor electrically connected to the gate line andthe second video signal line, and a second pixel electrode, wherein thesecond pixel electrode overlaps the first common electrode, wherein thesecond pixel electrode is connected to the second contact electrodewhich is connected to the second thin film transistor, wherein the metalfilm is not formed between the first contact electrode and the secondcontact electrode, in a plan view.